1. Field of the Invention
The present invention relates to a transmission that performs a gear change by selecting one from among multiple transmission gear sets, and particularly to a transmission that reduces a torque interruption period in a gear change and that has a simple structure.
2. Description of the Related Art
Automatic transmissions for vehicles include one having a combination of multiple planetary gear sets and a continuously variable transmission (CVT) employing a variator such as a chain variator, belt variator, and troidal variator. These automatic transmissions have not yet reached the level of manual transmissions, in which multiple gear sets arranged between a pair of rotating shafts are sequentially switched from one to another, in terms of transmission efficiency, weight reduction, and compactness.
To address this situation, an automatic transmission has been proposed in which an actuator performs shifting, selecting, and clutching operations that are performed manually in a manual transmission. This automatic transmission, however, needs to temporarily disengage the clutch before performing a gear change, and thus the torque interruption period is long.
Furthermore, a double clutch transmission (DCT) has also been proposed that includes two separate clutches and drive shafts for odd and even gear speeds. The DCT performs gear changes by switching between these clutches and drive shafts. However, the DCT has a complex structure and a large weight.
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-536713 describes the following transmission, which is an example of the conventional technology relating to a highly efficient transmission causing a short driving interruption period. Specifically, the transmission causes substantially no torque interruption and performs instantaneous gear changes by sequentially switching engagement states of first and second gear members included in each of gears, which are supported on a rotating shaft so as to be rotatable relative to the rotating shaft. The first gear member transmits a driving force in one rotational direction and the second gear member transmits a driving force in another rotational direction.
The transmission described in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-536713 includes a selector mechanism that has gear members between first and second gear ratios, between third and fourth gear ratios, and between fifth and sixth gear ratios.
The above transmission can perform instantaneous gear changes between first and second gear ratios, between third and fourth gear ratios, and between fifth and sixth gear ratios. However, as to the gear changes between second and third gear ratios and between fourth and fifth gear ratios, it is only after engagement members of the gear ratios with which the engagement members are engaged before the gear changes are moved to neutral positions that the transmission can start driving the engagement members of the gear ratios with which the engagement members are engaged after the gear changes. Thus, the gear changes between these gear ratios take more time.